Essential data for the automatic operation of a unit for sweetening kerosene or certain petroleum cuts, is the knowledge of their mercaptan sulfur content. More precisely, it is necessary to know the mercaptan content of the feed entering the unit, in order to adjust the air flow necessary for oxidation in the reactor, and the mercaptan content of the product at the outlet of the unit in order to meet specifications.
The object of the invention is, therefore, to provide a method and an apparatus for automatic titration of mercaptans, in an industrial sweetener unti for petroleum cuts.
Among the methods used in the laboratory, the argentimetric method consists in titrating the mercaptans by silver salts, and running a potentiometric detection of the end of the titration, according to the reaction: EQU R SH+Ag.sup.+ .fwdarw.R SAg+H.sup.30
A variation of this titration, which is of particular interest with a view to automation, is the coulometric generation of the Ag.sup.+ ion in the electrolyte solution by anodic oxidation of a metal silver gauze. The number of coulombs necessary for the titration is proportional to the quantity of mercaptans originally present in the solution.
Coulometric titration lends itself well to automation and since it requires no preparation of a reagent, it is not limited by the range of concentration of the mercaptans, and their molecular mass is not a factor. The precision is high. The titration times with a pilot-operated coulometer are short.